It's less of a hack and more of a simple override. You just put the disk in, activate it, then take it out and put in the outer region game and it works.
I know this thread has been mostly inactive for a while but tbh I'm suprised MP2 did comparitively badly - it is the highest ranked on TheTopTens "Best Mario Party Games" and it is the only one of the original N64 trilogy I have access to thanks to the Wii U VC. Any thoughts on why it didn't do better?